Servo or Stepper for watch winder using Arduino?

Hi everyone,

I started a project building a watch winder using Arduino.

At the moment I am using 4 DC motors controlled through 2 x L293DNE controllers.

What I want to do is to change those DC motors with TOWERPRO SG-90 Micro Servo (that I want to hack so it go full 360) or with a stepper (the stepper comes with a ULN2003 driver).

The motors I am looking at are:

stepper - http://www.instructables.com/id/BYJ48-Stepper-Motor/
servo - TowerPro SG90 Servo Specifications and Reviews

My question is:
Which one is better taking into consideration that what I want is a slow rotation (6 RPM), different direction of rotation and the motors should handle the weight of a light wooden cylinder with two watches in it.

I forgot to mention that I am also using a time module ( to start the motors at certain hours for certain period of time) and a rotary switch ( to tell the motors which direction)

Thank you very much

I think for your project a stepper would be the best bet.

Also there are already servos that run 360. That will be much easier than hacking one.

I would try a servo to start with.

They are much cheaper because a stepper motor also needs a stepper motor driver board; and they are much easier to program and easier to install.

If the watch can be wound with a to and fro movement you could probably get by with a 180 deg servo.

...R

I read that stepper don't have high torque comparing to servo. The motor has to rotate two watches ( plus the support) which might weigh up to 500 grams.

Another question is can both of them be controlled to run constantly at a low speed for a certain period of time?

Robin has a point if the to a friend works a servo is gonna be easier. Although steppers are free these days. Smash an old printer and get a 2$ darlington array or h bridge or even a hand full of transistors steppers are easy to run but a servo will be super easy.

drksam:
Robin has a point if the to a friend works a servo is gonna be easier.

Predictive text problem ?

Although steppers are free these days. Smash an old printer and get a 2$ darlington array or h bridge or even a hand full of transistors steppers are easy to run but a servo will be super easy.

Lots of printers just use cheap DC motors with encoders and (presumably) expensive software.

I doubt if printers need high-torque motors and high torque steppers don't work with darlington arrays or h-bridges.

Leaving aside the printers, you can get some very high torque steppers - all you need is money.

I don't understand why the weight of the watches is relevant. Surely all that matters is the torque needed to turn the winder - have you made any attempt to measure that?

...R

Yea productive text problem should have proof read it. It was to and fro.

And yes newer printers use dc motors and generaly poor components to cut cost. There are lots of really nice steppers inside of older printers electronic typewriters even scanners. I like them because you can find most of what you need to do some cool prototype projects. Sometimes you can even find the driver Ic on the board and take it too. But as long as your produce the correct pulses you can drive them lots of ways. Given that the quality of travel may suffer but even at that there are lots of high power stepper drivers available from places like digikey.